WO2013007484A1

WO2013007484A1 - Monochromatic x-ray source

Info

Publication number: WO2013007484A1
Application number: PCT/EP2012/061786
Authority: WO
Inventors: Oliver Heid; Timothy Hughes; Svetlana Levchuk
Original assignee: Siemens Aktiengesellschaft
Priority date: 2011-07-14
Filing date: 2012-06-20
Publication date: 2013-01-17
Also published as: DE102011079179A1

Abstract

The invention relates to an arrangement for generating X-rays and to an X-ray device comprising an electron source (1), an anode (20) which emits X-rays upon interacting with impinging electrons, and a collector (3) which slows and intercepts the electrons that penetrate the anode (20). The further interaction of said electrons, for example with the shielding of the arrangement, is prevented by slowing and intercepting the electrons after said electrons pass through the anode (20), and the undesired generation of additional bremsstrahlung is minimized. Power losses are also minimized. Characteristic X-rays of different energies can be generated in a manner that is adapted to the respective diagnostic use or requirement with respect to the size of the patient using an arrangement of multiple targets (21) with materials of different atomic numbers on the mounting (22) of the anode (20).

Description

description

Monochromatic X-ray source, the present invention relates to an arrangement for the generation ^¬ supply of X-rays and an X-ray device.

Previously known X-ray sources are, for example, X-ray tubes, which generate a wide wavelength spectrum of X-ray radiation. In particular, the bremsstrahlung is included in the wavelength spectrum. For various applications, in particular in medical diagnostics, however, the minimization of the X-ray dose with the same image quality is the highest goal. To generate good contrast-rich X-ray images, the characteristic X-ray radiation is decisive. The Bremsstrahlung should be reduced.

So far, it has been necessary to use large amounts of contrast agents to improve the image quality, in particular the contrast, in particular iodinated contrast media.

Previously known approaches to dose minimization by reducing the bremsstrahlung work with a filtering of the radiation, for example by metallic filters. This has ever ^¬ but that this also the characteristic radiation in the spectrum is significantly reduced with the disadvantage.

It is therefore an object of the invention to provide a source of X-radiation which does not emit disturbing Bremsstrahlung, which would have to be filtered for diagnostic applications.

The object is achieved by an arrangement according to claim 1 and by a device according to claim 13. Advantageous embodiments of the invention are the subject of the dependent claims. The arrangement according to the invention for generating X-ray radiation comprises an electron source for emitting an electron beam, an anode and a collector. In this case, the electron source and the anode are designed such that upon application of a positive electrical potential to the anode, electrons from the electron source can be accelerated in the direction of the anode. As an electron source can, for. Legs

Electron gun or a cold cathode can be used. An electron source thus supplies the electrons, which are accelerated towards the anode. The anode is so out ^¬ staltet is that emitted electrons upon interaction with X-rays from the anode and the collector is so arranged and constructed that advertising electrons which penetrate the anode, braked by the collector and collected the. The arrangement with the collector has the advantage that all braked and trapped electrons can not generate any further Bremsstrahlung within the arrangement. That is to say that the slowing down and interception of the electrons passed through the anode reduces the bremsstrahlung which would or would only arise in the system after penetration of the anode. Another advantage of the arrangement with the collector is the reduction of heat generation by interaction of electrons in the shielding material. The collector is therefore not just a standard shielding of the electrons. The arrangement has an active collector which decelerates and collects the electrons, so that electron losses prevented ^¬ the, no additional bremsstrahlung is formed in a shield and thus the heat generation is minimized.

In an advantageous embodiment of the invention, the collector of the arrangement is designed as part of an electrical circuit, so that the trapped electrons are held in the circuit, whereby electrical power losses are minimized. The electrons are therefore not verlo ^¬ reindeer, but can the collector as part of the Circuit is switched, the X-ray generation are fed back. As a result, the ^arrangement according to the invention is highly electrically effective. Pay particular attention to the collector of an electric Po ^¬ tential applied. This advantageously serves to decelerate the incoming electrons. The collector is designed in particular so that the incoming electrons an electric field, which is effected by this applied electrical potential, pass through and are decelerated therein. In particular, the voltage applied to the collector also causes the electrons passing through the anode to be aligned with the collector. This has the advantage that when hitting the collector or on a shield after passing through this electric field, the electrons have only so low energies that no or at least hardly Bremsstrahlung is generated.

An alternative method for reducing the bremsstrahlung of an X-ray source is known from US Pat. No. 7,436,931 B2. This describes a monochromatic Röntgenquel ^¬ le, which makes use of the directed extraction of the characteristic radiation. However, the electrons run in this embodiment in a substructure under the anode, in which they are slowed down. However, this substructure must be supplied with a cooling system, since the impinging electrons provide there for a high heat development by interaction with the material, which in turn can generate boundary radiation. Such a configuration is therefore extremely inefficient in terms of heat and heat.

In a further advantageous embodiment of the invention, the anode comprises at least one thin target layer whose layer thickness is less than the electron range in the material of the layer. This target layer of the anode is used to generate the characteristic X-radiation. The small layer thickness ensures that only a minimum of bremsstrahlung is generated at all. Of course, one has to certain layer thickness be ensured in order to generate the ge ^¬ desired intensity of the characteristic radiation in the target layer. If the layer thickness but less than the electron range in the material, many electrons are still sufficiently high energy by the mate rial ^¬ penetrate without much interaction by the fact

To generate bremsstrahlung. The electrons can then be decelerated and collected with the collector. In other words, the anode is in particular designed such that it serves exclusively to generate the X-radiation, in particular the characteristic X-radiation, and not also to decelerate the electrons. For example, for tungsten as a target layer material, the layer thickness would advantageously be 8 μm or less.

The target layer comprises in particular a material which has an atomic number between 42 and 74. Materia ^¬ lien this atomic number are suitable for the generation of X-rays. These are, for example, molybdenum with the atomic number 42 or tungsten with the atomic number 74.

In a further advantageous embodiment of the invention, the anode comprises a holder on which the thin tar ^¬ getschicht is arranged. The holder is a

Disc whose thickness is less than the Elektronenreichwei ^¬ te in the disc material. That is, the holder is in particular a flat disc, on which the thin target layer can be applied. The holder may in particular have different geometries. The thin target layer is in particular a metal layer, which can be applied to the mount, for example, by known deposition methods. For example, the holder may be a diamond wheel. The thickness of the holder is in particular ^¬ special again lower than the electron range in the disc material. This has the advantage that even in the Hal ^¬ sion little bremsstrahlung is generated by interaction with the electrons. The electrons should leave the holder as far as possible with only little interaction and only be slowed down and collected by the collector. The anode is thus preferably so thin that it is penetrated by the electrons. Due to the small overall thickness of target layer and holder, the advantage is thus ensured of generating only minimal bremsstrahlung. In particular ^¬ sondere the thinness of the support also causes mi ^¬ nimierte heat development due to electron interaction.

The material of the holder has in particular an atomic number of 15 or lower. It is just about not to produce unwanted X-rays, no additional characteristic radiation of different wavelengths.

Requirements for the holder are accordingly in particular their thickness, the z. B. is chosen lower than the

Range of electrons in this material. In addition, the atomic number of the support material should in particular be less than 15. In a further advantageous embodiment of the invention, the anode has a plurality of target layers, which has materials of different atomic number. This has the advantage that with this arrangement, characteristic X-radiation of different energy ^¬, depending on the target material can be produced. Different X-ray energies are necessary, for example, in order to adapt the radiation to the respectively required application or, in the case of diagnostic applications, to adapt the radiation energy to the patient. Depending on the dimensions of the patient, the energy of the X-ray radiation has to be adjusted in order to achieve a sufficiently high contrast

Image for diagnosis. This is possible in particular with the present arrangement for generating X-radiation with different target materials. More particularly, the materials of the target layers, in particular at least 10 chairs vary in their atomic number of at least 3, such as at least 5, the Atomzah ^¬ len too close together, this also applies to the generatable characteristic radiation too. As a pair of target materials, for example molybdenum and gadolinium or gadolinium and tungsten come into question. In a further advantageous embodiment of the invention, the electron source is arranged to the anode and / or is in the arrangement of a device for guiding an electron beam comprises, so that the electrons can be accelerated perpendicular to the anode. This has the advantage that the electrons in the shortest path for the penetration of the

Anode can be sent, and thus in the anode only generate mi ^¬ nimal bremsstrahlung and ensure heat. In particular, the anode and the electron source are arranged to be movable relative to each other, so that each target layer can be positioned in the electron beam. This has the advantage that characteristic X-ray radiation with adjustable energy can be generated with one and the same arrangement having only one electron source and one collector and only one anode structure.

Preferably, the arrangement also has a shield, which is connected to the anode so that all not positioned in the electron beam target layers are shielded by this shield so that the target layers are not contaminated with material of the positioned in the electron beam target. The arrangement with several different target layers allows the setting of a characteristic wavelength. This arrangement is of particular advantage for diagnostic ^methods in which different x-ray energies are used. In addition to the adaptation of the X-ray energies to the dimensions, such as weight and volume, of a patient, the different images can also be advantageously used in subtraction angiography. Thus, the X-ray device according to the invention comprises a ^¬ An order for generating X-radiation with an electron source for emitting an electron beam, an anode and a collector. Electron source and the anode are configured to be accelerated upon the application of a positive electrical ^¬'s potential to the anode electrons from the electron source toward an anode, wherein the anode is configured to emit X-ray radiation upon interaction with electrons and wherein the collector so on - ordered and designed to electron, which penetrate the anode, decelerate and catch. All other embodiments of the arrangement are also encompassed, for example, by the X-ray device. This then also has the ^{¬ written} benefits of the invention.

Accordingly, the arrangement according to the invention particularly improves the diagnostic applications of X-ray radiation, such as, for example, subtraction angiography. By Reducing ^¬ te bremsstrahlung and characteristic radiation very energy exact amount can be reduced to iodinated contrast agents.

Embodiments of the present invention will be described by way of example with reference to ^FIGS . 1 to 4 of the attached drawing. Showing:

FIG. 1 shows the schematic arrangement of electron source 1,

Anode 20 and collector 3 and

Figure 2 to Figure 4 shows the schematic arrangement with an anode 20 with multiple targets 211, 212nd

FIG. 1 schematically shows a cross section through the arrangement for generating X-ray radiation. In this case, the electron source 1 is generally shown as a rectangle. This can be arranged on an axis with anode 20 and collector 3, as shown in Figure 1, but can also be arranged laterally offset from this axis. In particular, the electron source 1 can not initially be applied directly to the anode 20. be directed and the emitted electron beam is then z. B. directed by another device for deflecting the electrons to the anode 20. The anode 20 is greatly simplified as a rectangle Darge ^¬ provides. From the side of the electron source 1, the anode 20 comprises the target 21, a thin layer on the holder 22. In the electron direction behind the anode 20, the collector 3 is still shown. This is in turn shown greatly simplified as a rectangle with trapezoidal cutout. This section indicates the inlet for the electrons. In this cavity, which is shown in cross-section, an electromagnetic field for decelerating the electrons can be generated.

From the electron source 1 to the anode 20, therefore, the electrons can reach arbitrary paths, but the electron source 1 and the anode 20 are arranged and configured so that the electron beam strikes the anode 20 perpendicularly. In the holder 22, it is in particular a flat disc on which the thin target layer 22 is playing as applied as a coating at ^¬. The material of the holder 22 is a material of low atomic number, in particular less than 15, since it is intended to generate only the lowest possible X-ray radiation by interaction of the electrons. In particular, the material of the holder 22 is a diamond disk. The coating with the target material 21, however, has a high atomic number, in particular between 42 and 74.

In contrast to previous arrangements for the generation of X-radiation, the arrangement with the collector 3 has the advantage that it is part of the circuit. On the one hand, the collector 3 can be brought to an electrical potential, which decelerates the electrons before impinging on further material. This has the advantage of minimizing the heat generated by the electron interaction. Furthermore the further generation of Bremsstrahlung is minimized by interaction of the electrons with the collector material. By the collector 3 as part of the circuit, the electrons are not only collected, but can continue to be used. That is, by collecting the electrons, the entire assembly becomes electrically much more efficient than previous arrangements in which the once-emitted electrons were lost. FIG. 2 shows, in the same schematic representation as in FIG. 1, an embodiment of the arrangement with a plurality of target layers 211, 212. The anode 20 is shown again schematically as a rectangle, with the holder 22 on which the thin target layers 211, 212 are applied. For this task brin supply known coating methods can be used, depending on which target material to it han delt to ^¬. Between the target layers 211, 212, in turn, a vertical barrier, a shield 23, is shown very schematically. This shielding, shown in cross-section, is intended to ensure contamination of the respectively unused target 211, 212.

Figures 3 and 4 show the same structure as in Figure 2, except that each one of the target layer 211 was 212 sitioned so po- that the electron makes this vertically and centrally enters after passing through the anode 20 into the Kol ^¬ lecturer. 3 In FIGS. 3 and 4, the direction of the electron is indicated by an arrow from the electron source 1 to the anode 20. The electrons are accelerated to the anode with different energies El, E2, ie different anode potentials. Depending on the material of the target layer 211, 212 a entspre ^¬ sponding acceleration voltage for the electrons from the electron source 1 is applied to the anode 20th In accordance with this difference in acceleration voltage, the electrons in the respective target material can generate characteristic X-radiation. The electrons that have penetrated the anode 20 and then hit the collector 3 can turn there be braked with adjusted potential. That is, the Kol ^¬ lecturer 3 is especially designed so that it can decelerate electrons of different energy. For example, tungsten can be used as the second target material 212 ^¬ the first target material 211 and molybdenum. While the characteristic K _a -line energy for tungsten is around 59 keV, for molybdenum it is around 17 keV. Accordingly, the electrons are accelerated to the molybdenum target with a lower anode voltage than to the tungsten target. For example, electrons of 2 to 3 times, in particular up to 4 times, energy are used. The anode voltages are therefore in particular in a range between about 40 kV up to 240 kV.

Claims

claims

Arrangement for generating X-radiation with

an electron source (1) for emitting an electric ^¬ nenstrahls,

an anode (20) and

a collector (3),

wherein the electron source (1) and anode (20) are designed so that upon application of a positive electrical potential to the anode (20) electrons from the electron source (1) in the direction of the anode (20) are accelerated, wherein the anode (20) designed is to emit X-rays when interacting with electrons and

wherein the collector (3) is arranged and configured electrons that penetrate the anode (20), ERS ^¬ braking and catch.

2. Arrangement according to claim 1, wherein the collector (3) is a part of an electrical circuit and configured to hold the trapped electrons in the circuit and thereby minimize electrical power losses.

3. Arrangement according to claim 1 or 2, wherein an electric potential can be applied to the collector (3).

4. Arrangement according to one of the preceding claims, wherein the anode (20) comprises at least one thin target layer (21) whose layer thickness is less than the electron range in the material of the layer (21).

5. Arrangement according to claim 4, wherein the target layer (21) comprises a material having an atomic number between 42 and 74.

6. Arrangement according to claim 4 or 5, wherein the anode (20) comprises a holder (22) on which the thin target ^¬ layer (21) is arranged, wherein the holder (22) is a disc whose thickness is ge ^¬ ringer as the electron range in the Scheibenma ^¬ TERIAL.

7. An assembly according to claim 6, wherein the material of the holder (22) has an atomic number of 15 or lower.

8. Arrangement according to one of the preceding claims, wherein the anode (20) comprises a plurality of target layers (211, 212), which comprise materials of different atomic number.

9. Arrangement according to claim 8, wherein the materials of the target layers (211, 212) differ in their atomic number by at least 3, in particular at least 5.

10. Arrangement according to one of the preceding claims, wherein the electron source (1) is arranged to the anode (20) and / or wherein the arrangement comprises a device for guiding an electron beam, which is designed so that the electrons perpendicular to the anode ( 20) are accelerated ^¬ bar.

11. Arrangement according to one of the preceding claims, wherein the anode (20) and the electron source (1) are arranged relative zueinan ^¬ movable, so that each target layer (211, 212) is positionable in the electron beam.

12. Arrangement according to one of the preceding claims, wherein the anode (20) has a shield (23) through which all not positioned in the electron beam target layers (211, 212) are shielded so that they are not covered with material of the electron beam positioned in the target layer ( 211, 212) are contaminable.

13. X-ray device with an arrangement according to one of claims 1 to 12.